title: Short-term disturbance by a commercial two-dimensional seismic survey does not lead to long-term displacement of harbour porpoises.
abstract: Assessments of the impact of offshore energy developments are constrained because it is not known whether fine-scale behavioural responses to noise lead to broader-scale displacement of protected small cetaceans. We used passive acoustic monitoring and digital aerial surveys to study changes in the occurrence of harbour porpoises across a 2000 km(2) study area during a commercial two-dimensional seismic survey in the North Sea. Acoustic and visual data provided evidence of group responses to airgun noise from the 470 cu inch array over ranges of 5-10 km, at received peak-to-peak sound pressure levels of 165-172 dB re 1 µPa and sound exposure levels (SELs) of 145-151 dB re 1 µPa(2) s(-1). However, animals were typically detected again at affected sites within a few hours, and the level of response declined through the 10 day survey. Overall, acoustic detections decreased significantly during the survey period in the impact area compared with a control area, but this effect was small in relation to natural variation. These results demonstrate that prolonged seismic survey noise did not lead to broader-scale displacement into suboptimal or higher-risk habitats, and suggest that impact assessments should focus on sublethal effects resulting from changes in foraging performance of animals within affected sites.
authors.affiliation: Lighthouse Field Station, Institute of Biological and Environmental Sciences, University of Aberdeen, , Cromarty IV 11 8YL, UK, Kongsberg Maritime Ltd, , 11 The Briars, Waterberry Drive, Waterlooville, Hampshire PO7 7YH, UK, WWT Consulting, , Slimbridge, Gloucestershire GL2 7BT, UK, Department of Physics, University of Bath, , Bath, Somerset BA2 7AY, UK.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Thompson
authors.forename: Kate L
authors.initials: KL
authors.lastname: Brookes
authors.forename: Isla M
authors.initials: IM
authors.lastname: Graham
authors.forename: Tim R
authors.initials: TR
authors.lastname: Barton
authors.forename: Keith
authors.initials: K
authors.lastname: Needham
authors.forename: Gareth
authors.initials: G
authors.lastname: Bradbury
authors.forename: Nathan D
authors.initials: ND
authors.lastname: Merchant
mesh_terms: D063147:Animal Distribution; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D017753:Ecosystem; D019652:Extraction and Processing Industry / Q000379:methods*; D008954:Models, Biological; D009622:Noise / Q000009:adverse effects*; D009659:North Sea; D050741:Phocoena / Q000502:physiology*; D011312:Pressure / Q000009:adverse effects; D012606:Scotland
keywords: Phocoena phocoena; acoustic disturbance; marine mammal conservation; marine spatial planning; oil and gas exploration